Sputtering is a process that uses ions of an inert gas, sometimes in the presence of a reactive gas, to dislodge atoms from the surface of a target material. The atoms then are electrically deposited to form an extremely thin coating on a glass, metal, plastic, or other surface. Sputtering has been used to deposit hard substance coatings on tools, molds, and wear parts to improve their surface characteristics and length of useful life. Some such coatings are suitable for decorative purposes. A number of coatings have been developed, one of which, boron carbide, is described in U.S. Pat. No. 4,716,083.
Sputtered coatings typically are applied in a gas plasma in a vacuum at relatively low temperatures. Reactive gases can be included in the plasma, if desired. Sputtering is a highly desirable process for applying hard substance coatings to various metal tools, wearparts, and the like because the coatings can be formed and are adherent to the substrate while avoiding significant changes in the properties of the substrate material that can be caused by elevated temperature.
As described in U.S. Pat. No. 4,716,083, it is desirable to provide an atomically clean surface on the portion of the tool or other substrate that is to be coated to facilitate formation of a uniform coating that is adherent to the substrate surface. Foreign material on the substrate surface, including outgassing from the substrate surface, can cause premature failure of the coating or a lack of adherence.
There are several methods known to the skilled artisan for providing an atomically clean surface for sputtering. In accordance with one method for providing an atomically clean substrate surface, the substrate is degreased with a chlorinated hydrocarbon degreaser. Thereafter, the substrate is rinsed in methanol and subjected to either plasma or dry chemical etching. However, organic solvents typically are not employed at the present time due to environmental considerations. Aqueous solvents are preferred.
As an example of plasma etching, after the articles to be coated have been rinsed in various solutions to prepare their surfaces, the articles may be placed in a vacuum chamber. The chamber is evacuated. An inert gas, and sometimes a reactive gas, is introduced into the chamber, and current is applied to create a plasma. The ionized atoms of gas impinge on the articles in the vacuum chamber and remove surface contaminants, such as oils or greases and adsorbed gases that may remain after the typical solvent cleaning steps. In addition, gas sputtering can be used to activate surfaces by removing oxides from metal surfaces or creating free radicals on polymeric surfaces.
After the sputter etching step is completed, then the hard substance coating is applied to the substrate. After coating is completed, the articles having the sputtered coating thereon can be removed from the chamber.
Various attempts have been made to increase the efficiency of sputter coating methods and apparatus for specific applications. For example, U.S. Pat. No. 3,968,018 describes an apparatus and a method for sequentially cleaning and coating small articles, such as treating an array of razor blades, by moving the blades successively through one chamber for cleaning, one for coating, and one for serving as a vacuum lock so that the blades can be transferred successively from one chamber to another without being contaminated during cleaning and coating.
As disclosed in U.S. Pat. No. 3,968,018, the sputtered coating atoms are deposited on the exposed edges lying along the upper surface of an array of razor blades or other articles. A series of fixtures or holders for the razor blades is generally illustrated and described.
It is important in any sputtering operation that the surfaces of the articles that are to be coated be uniformly exposed to the plasma so that a uniform coating will be formed on the exposed surfaces of the articles. However, articles having somewhat complex shapes or having a variety of shapes, as in a collection of different articles, present obstacles and difficulties to increasing the efficiency by which such articles may be sputter coated. Typically, batch operations are employed that are somewhat slow and tend to be labor intensive, reducing the number of articles that can be coated in a given period of time.